The present invention generally relates to a method for cooling an internal combustion engine, more particularly relates to a method for controlling cooling fans for an internal combustion engine on a vehicle.
A method to operate cooling fans is presented in Japanese Patent Application Publication no. H11-107753. In particular, the method describes differentiating a combustive vibration frequency of the engine which is a nth order frequency component of the engine rotation (e.g. a second order component (second order vibration) in a case of four cylinder four stroke engine) and a rotational vibration frequency of cooling fans from each other by lowering rotational speed of the two cooling fans when the engine coolant temperature is lower and while the engine is idling.
The inventors herein have recognized disadvantages of the above-mentioned method. Namely, lowering the fan speeds may lead to lower the cooling air flow and thereby reduce the cooling capacity of the radiator and/or condenser. And although it may be possible to improve the cooling system capacity by increasing the fan diameter and the electric motor output, increasing the fan inertia can also increase the amplitude of the rotational fluctuation of the fan. Furthermore, resonance between the two cooling fans operating at the same rotational frequencies can become a problem as a new source of vibration and/or noise during engine idle where such noise may be undesirable.